Unlike JDS Labs and iFi before, I certainly had to add aune to our list of manufacturers whose products have been covered on TechPowerUp. aune is the Hi-Fi brand of Wuhan Ao Lai Er Technology Co., Ltd., which in itself is only known for the aune brand at this time globally despite being founded in 2004. I suppose it's much simpler to market "aune," and the marketing does take advantage of the rounded letters to inspire product design as well. It is a brand predominantly known for its desktop and portable class DACs and amplifiers, often going further in feature set and pricing to come off as more premium than most of its Chinese neighbors we've reviewed to date.
Today, we examine the recently announced aune BU2, a premium portable Bluetooth DAC/amp that has quite a lot going on inside, which is why this happens to be the physically largest such portable unit covered, almost to where it is barely pocket-friendly. The full product name confirms there is Bluetooth connectivity, making for a DAC/amp that can be used wired or wirelessly. The latter makes wired portable devices in particular somewhat wireless, and there is a balanced output to power more power-hungry full-size headphones, too. Let's find out what makes the aune BU2 so imposing, and thank you HiFiGo for providing this sample for us to test and take apart—literally!
Packaging and Accessories
The product box comes with a plastic seal all around and has the customary HiFiGo sticker I've seen on samples shipped from the retailer. Removing it reveals a relatively large box for a portable unit, which is not surprising given this is a large unit. The outer sleeve is predominantly white with the company logo and product name on the front going with a simple line render of the product and salient marketing features. I do like the illustration on the back clearly depicting how the aune BU2 is to be used. The inner box can be slid out the top or bottom.
This inner box is all black and made out of thicker cardboard, with the logo in silver lettering on the front. The lid opens up to reveal the contents inside, with a thin foam lining on the underside of the lid for further protection. There is a multi-language quick start guide that goes over the various components of the aune BU2, and I highly recommend going through it since the BU2 has a lot of pre-programmed features onboard and no app support. There is a contact card that has warranty information in addition to finding the social media pages for aune. The BU2 comes packaged into a cutout in thick foam, and a separate box contains the accessories. aune is fairly generous in this regard, and we see an L-shaped Type-C to Type-C cable, longer Type-C to Type-A cable, low-profile female Type-C to male Lightning adapter, and fancy 4-core braided 2.5 mm TRRS male to 4.4 mm TRRS female adapter cable for a balanced connection when you do not have the 2.5 mm plug on your IEM/headphone cable.
I don't know what I was expecting when I was first asked about whether I would like to review the aune BU2, but it was not this! Never mind the large form factor—this is quite unlike anything else I have used thus far. It's still portable in that there is a large battery inside for wireless connectivity in addition to the "cleaner" battery power than USB, and the predominantly black ABS plastic enclosure makes for a lighter product than expected even with all the hardware inside. Look at that cutout in the middle at the top, if you will, where there is a knurled multi-function wheel. I do wish the gap were slightly larger, or the wheel extended outward further since it is not the easiest to rotate even with my hands that run slightly smaller than average. But I understand the deliberate design to keep everything contained within the footprint of the enclosure, and it's a compromise where I just happen to find myself on the other side from aune. Then there's an integrated display with branding on either side. The branding continues on the back, but in a neat enough manner not to be distracting.
The bottom side is where you will find two separate Type-C ports, including one for charging. This means the other one used for wired connectivity will not charge the internal battery whatsoever. I do like this implementation since you don't need to worry about running down the battery lifetime with continual charges and, in the absence of an app to change this as with the likes of FiiO and Qudelix, the dual USB implementation is the best way forward. As a 1 A charging port, charging is also faster than with contemporaries. The opposite side contains the two headphone outputs, including a 3.5 mm single-ended TRS jack and 2.5 mm balanced TRRS output. The latter is where I see the aune BU2 unfortunately not lasting the test of time as the larger form factor would easily allow for the increasingly more common 4.4 mm balanced output instead. IEMs increasingly come with cables that can swap between 2.5/3.5/4.4 mm outputs, but good luck finding headphone cables using the 2.5 mm connector for a balanced connection. The provided adapter cable feels like a bone being thrown to soothe an angry dog without actually solving the issue. Between the two is a button tied to the wheel from earlier, clicking which goes through different functions of the aune BU2 akin to what we saw recently with the iFi GO blu that provides both the 4.4 mm output and a better wheel/button implementation despite its smaller size.
After all testing was completed, I disassembled the aune BU2 for a closer look at what's inside. Doing so means removing the four Torx-head screws on the back, and at this point, you realize that three primary sections are held together by these screws. The back plastic panel has the relatively massive 11.1 Wh battery glued to it, which incidentally makes me feel like all wireless keyboards could be doing much, much better for their size. For a direct comparison, the 11.1 Wh battery is a 3000 mAh battery on the 3.7 V rail it's operating on, which is also significantly higher than any other portable DAC/amp I've tested to date. There is an internal cable to dislodge from the PCB on the back, which is otherwise bare of anything else noteworthy.
The other side is where the real action takes place, including with the rotary knob and display modules connected to the PCB and associated controllers, and an STMicroelectronics STM8S105K4 8-bit microcontroller. Solder quality is exceptional, so much so that I'd be lying if I said a limited edition with a polycarbonate see-through enclosure would be a bad idea. A lot is going on here, although I was somewhat disappointed I could not identify the Bluetooth transceiver under a metal EMI/RFI shield. A ESS Sabre ES9318 premium-class dual-DAC chip is used, with each DAC tied to a headphone output, and aune is using the same single-to-dual positive/negative voltage power supply output as on the previous BU1 to make for a total of two DACs in parallel and four amplifiers to power everything.
The two DACs are associated with two low-jitter 45M/49M oscillators for clock synchronization. There's also the same XMOS U30870C10 as in the JDS Labs Atom DAC+—an XMOS XU208 USB bridge with the xCORE 32-bit multi-core microcontroller that has successfully been used for USB audio Class 2 implementations. The aune BU2 is capable of providing up to 32-bit 768 kHz PCM playback, and it supports up to DSD512 native decoding as well. It also boasts a noise floor as low as 3.16 µV, THD+N of 0.0000145%, SNR of -120 dB, channel matching of +/- 0.5 dB across 20 Hz-20 kHz, and has independently verified numbers vouching for this to where it's effectively an excellent desktop-class DAC in a portable form factor.